The frames of heavy duty trucks are typically suspended on torque reactive rear suspensions. When torque is applied to the truck drivetrain, the frame of the truck tends to raise and move away from the drive axle. This frame motion causes many problems, including wheel hop and driveline misalignment. With recent advances in engine technology, higher horsepower and increased torque capabilities have exacerbated this frame motion and its attendant problems. In particular, increased driveline misalignment can cause vibration that is transmitted to the cab of the vehicle to the detriment of the ride quality experienced by the driver.
Several techniques have been used in the art to adaptively control the position of the frame in vehicles. For example U.S. Pat. Nos. 5,529,153 and 4,743,046 to Smith and Schnittger, respectively present vehicle suspension systems featuring damping components whose damping characteristics vary as a function of vehicle position, i.e. provide a stiffer suspension when vehicle tilt is above a predetermined threshold. U.S. Pat. No. 5,785,345 to Barlas et al. describes a heavy duty truck suspension that includes a hydraulic lock structure that is selectively locked when frame height raises above a nominal ride height. One of the hydraulic lock structures disclosed features a pair of hydraulic cylinders disposed between the vehicle frame and suspension. The hydraulic cylinders are in fluid communication with a fluid reservoir to provide cushioning when the vehicle is operating at nominal ride height, and a control valve blocks the flow to the reservoir when the vehicle is experiencing frame rise, thereby locking the frame with respect to the suspension once the frame has risen above a threshold amount.
While it is believed that these systems provide an improved amount of control over frame position during vehicle operation, these systems rely on the position of the frame to trigger the control effort. As such, the vehicle must experience a certain amount of frame motion beyond a desired position prior to correction.